There are two main species of bedbugs:                Cimex lectularius (common bed bug); and        Cimex hemipterus (tropical bed bug).        
They appear to share the same behaviour patterns.
Bed bugs are parasites that preferentially feed on humans. They are a persistent pest and have developed a number of highly evolved abilities to remain close to humans. However, when humans are not available they will feed on other warm blooded animals such as rodents and birds.
Bed bugs were common in the UK prior to World War II, after which time widespread use of synthetic insecticides such as DDT greatly reduced their numbers. At one stage in the 1930's 25% of all homes in the UK were infested.
In the past decade, bed bugs have begun making a comeback across the world. Although they are not considered to be a major pest or health hazard they can be highly unpleasant to live with and can cause a severe lack of sleep. International travel and commerce are thought to facilitate the spread because eggs, young, and adult bed bugs are readily transported in luggage, clothing, bedding, and furniture. Bed bugs can infest aircraft, ships, trains, and buses. Bed bugs are most frequently found in dwellings with a high rate of occupant turnover, such as hotels, motels, hostels, dormitories, shelters, apartment complexes, tenements, and prisons. Adult bed bugs are brown to reddish-brown, oval-shaped, flattened, and about 0.4 cm to 0.45 cm long. Their flat shape enables them to readily hide in cracks and crevices.
Female bed bugs lay from one to twelve eggs per day, which are deposited on rough surfaces or in cracks and crevices. The eggs are coated with a sticky substance so they adhere to the substrate. Eggs hatch in around 10 days, and nymphs can immediately begin to feed. They require a blood meal in order to moult and develop into the next stage. Bed bugs reach maturity after five moults. Developmental time (egg to adult) is affected by temperature and takes about 21 days at 30° C. to 120 days at 18° C. The nymphal period is greatly prolonged when food is scarce. The adults' lifespan may be as much as 12-18 months and they are known to be able to survive for 12 months between feeds.
Bed bugs are fast moving insects that are nocturnal blood-feeders using a barbed spike to penetrate the skin by repeatedly hammering at the surface. Nymphs may become engorged with blood within three minutes, whereas a full-grown bed bug usually feeds for ten to fifteen minutes. They then crawl away to a hiding place to digest the meal. A full meal may take 3 or 4 days to digest.
Bed bugs hide during the day in dark protected sites; they prefer fabric, wood, and paper surfaces. They usually occur in fairly close proximity to the host, although they can travel relatively large distances. Bed bugs initially can be found in seams, and folds of mattresses, later spreading to crevices in the bedstead. In heavier infestations, they also may occupy hiding places further from the bed. They may hide in window and door frames, electrical boxes, floor cracks, baseboards, furniture, and under the tack board of wall-to-wall carpeting. Bed bugs often crawl upwards to hide in pictures, wall hangings, curtain pleats, loosened wallpaper, cracks in plaster, and ceiling mouldings.
There are many different insect traps and approaches to capturing small biting insects and they range widely in design.
A bed bug monitor trap is disclosed in US 20070044372. The main embodiment described discloses a trapping device comprising a corrugated layer and a first glue board, configured to immobilise insects, which is attached to the ridges of the corrugated layer. In a second embodiment there is disclosed a trapping device comprising a base and a lid covering the base defining a trap interior, a heating device provided within the trap and an adhesive surface provided within the trap interior.
The detailed description describes different attractant mechanisms including:                Pheromones;        Food attractants;        Tactile cues; and        Olfactory attractants.        
Whist under each heading a wide variety of options are considered, the application does not teach any benefit in making particular selections.
Thus, tactile cues include:                Textured materials;        Materials with a low heat transfer;        Vibration;        Heat (including radiant or infrared) and        Humidity.        
Other patent publications of interest include the following:
U.S. Pat. No. 4,168,591 which discloses an apparatus and method for attracting and killing mosquitoes and other similar insects. It teaches using heat and moisture as attractants. The apparatus comprises a heating coil which generates heat and helps generate moisture from a sleeve filled with water.
WO 00/03594 and WO 99/35908 both of which disclose insect killing systems optimized for mosquitoes which simulate the breathing and body heat from animals. Both use heat generating elements and a supply of liquid.
SE 535476 also discloses an insect trap which utilises water and heat to attract insects.
It is an aim of the present invention to provide a simple effective trap for small biting insects which does not have the disadvantages associated with the traps described, namely the provision of water in liquid form and an electrical source for heating. A separate and independent aim was to develop a purpose made chemical heat pad, which in addition to generating heat additionally generated moisture. In this regard commercially available head pads, for use as e.g. hand warmers, have not been designed to generate water vapour as well as heat.